1. Field of Invention
The present invention relates generally to the field of communications. More specifically, the present invention is related to intrinsically safe communications in a hazardous area.
2. Discussion of Prior Art
In the industrial automation market in recent years, Ethernet has become a standard choice for digital communication between various hardware devices. For Ethernet communications in Hazardous areas, customers use either a combination of specialized copper cable and connector or a fiber cable. There are very significant difficulties in using cables in hazardous areas. For electrical signals that are not intrinsically safe (I.S.) in hazardous area, the wiring regulations are very stringent and requires very specialized cables often requiring armor (for physical protection against cable cuts) and specialized methods of cable entry and termination. In the case of connectors for easy connection mechanism, the connectors must meet explosion-proof (or flame-proof) requirements. These specialized connectors are not offered for a wide range of applications and are expensive. In addition to these difficulties, the cables require maintenance as these are prone to damage. This increases the operational cost both in periodic maintenance and replacement of damaged cables.
In applications where it is not desirable or feasible to use the cable (because of distance, installation limitation etc.) wireless communication is being considered. Industry standard Ethernet-based wireless communication has become commercially acceptable and is gaining acceptance in industrial applications as well. However, there are a very limited number of solutions available for use in hazardous areas. Such prior art solutions involve the use of an explosion-proof box where the radio transceiver is mounted and the antenna is “attached” to the explosion-proof box. The signal strength indicators of the prior art are not designed for hazardous areas.
The following references provide general teachings for communicating in a hazardous area.
The patent to Hellman et al. (U.S. Pat. No. 5,992,436) assigned to Armstrong International, Inc. provides for a monitoring steam traps using RF signaling. Disclosed is transmitter 58 to provide a spread spectrum wireless communication link. Monitor and associated equipment are intrinsically safe and will not produce a spark or a heated surface sufficient to ignite or cause explosion of various hazardous material (see column 6 lines 35-40, 61-67).
The patent to Mansfield et al. (U.S. Pat. No. 6,404,609 B1) assigned to Micro Motion, Inc. provides for a circuit that reduces the numbers of components needed to transmit data from intrinsically safe to non-intrinsically safe circuits using opto-couplers. Disclosed is an intrinsically safe circuit 201 configured for supplying intrinsically safe power from a power supply in a hazardous environment (see abstract).
The patent to Lytollis (U.S. Pat. No. 6,751,076 B2) assigned to The MTL Instruments Group plc, provides for protection of intrinsically safe circuits. Disclosed is voltage sensor A1 and current sensor A2 and intrinsically safe circuits that operate within hazardous areas (see column 1 lines 8-9 and column 2 lines 59-61)
The patent application publication to Loechner (2002/0065631 A1) provides for a field device configured for wireless data communication. Discussed is the passive achievement of intrinsic safety through related design of electronics to avoid overheating and increased current/voltage (see paragraph 15). Discussed field device may communicate with the remote device 48 having a transmitter and/or receiver 52 for wireless data communication (see paragraph 65).
The patent application publication to Zielinski et al. (2003/0109937 A1) provides an intrinsically safe field maintenance tool. Disclosed is tool 22 that is able to transfer information using infrared data access port (see paragraph 22). Module 44 is replaceable in hazardous areas in a process plant and complies with intrinsic safety requirements by using energy limiting circuits to prevent sources of ignition (see paragraph 24).
The patent application publication to Kirkpatrick et al. (2004/0158334 A1) assigned to Rosemount Inc. provides for a two-wire field-mounted process device. Disclosed is a loop communicator 36 which can include suitable isolation circuitry to facilitate compliance with the intrinsic safety specification (see paragraph 23).
The patent application publication to Dungan (2002/0070869 A1), assigned to Gastronics', Inc., provides for a monitoring method. Disclosed is a monitor system 20 having a master station 22 and a plurality of monitor stations 24. The monitor station 24 has a radio 36 with antenna 70. The monitor stations 24 have explosion-proof housings 44. The gas sensor 66 (inside of stations 24) is of the intrinsically safe type (see FIGS. 1-3; and paragraphs 27, 29, 32, 35, 37, 50, and 58).
The patent application publication to Poon et al. (2003/0083038 A1) provides for a signal adapter. Disclosed is a signal adapter 103 having a radio transceiver located within an explosion proof container 107. The signal adapter outputs an intrinsically safe signal to an antenna 101. The output signal must not be capable of igniting an explosive material (natural gas) (see FIGS. 1-2; and paragraphs 4, 5, 15-17, 20-21, 31, and 33).
The patent application publication to Flasza et al. (2004/0066588 A1), assigned to Magnetrol International, provides for a process control instrument intrinsic safety barrier. Disclosed is an antenna 26 using a coaxial cable 28 having connectors 30 and 32. The first connector 30 is connected to the antenna 26. The second connector 32 is connected to a connector 34 located in a housing 22. An intrinsic safety (IS) barrier or circuit 78 is proximate the antenna connection 34 to guarantee that sufficient amounts of energy cannot be transferred into a tank (via the antenna) causing an explosion (see FIGS. 1, 3; and paragraphs 4, 8, 16, 31, 33, 35, 36, 39, 42, 44, and 48).
Whatever the precise merits, features, and advantages of the above cited references, none of them achieves or fulfills the purposes of the present invention.